1. Field of the Invention
This invention relates to a method of and apparatus for finishing coated papers enabling smooth, super-high-gloss coated papers to be produced.
2. Description of the Prior Art
Various methods have hitherto been available for finishing coated papers to impart high or improved smoothness and gloss thereto. In one method well known in the art as a gloss calendering method, an aqueous coating composition containing thermoplastic synthetic resin emulsion is applied to the surface of a paper web to form a coating layer or film and the coated paper web is subjected to finishing in two stages after the coated composition is dried at a temperature below the glass transition temperature of the thermoplastic synthetic resin emulsion, the finishing stages including a fir st finishing stage in which the coated paper web is passed over a finishing roll while the surface of the coating layer is brought into pressing contact with a mirror-like metal surface of the finishing roll heated to a temperature above the glass transition temperature of the emulsion, and a second finishing stage in which the coated paper web is passed over the finishing roll while the surface of the coating layer is brought into pressing contact with the finishing roll. The gloss calendering method described hereinabove has the advantages that coated papers of high gloss and smoothness can be produced without reducing bulk or thickness of the coating layer and that coated papers can be produced with high production efficiency. However, the gloss calendering method of the prior art is defective in that, although this method can produce high-gloss coated papers generally referred to as coated papers and art papers, it has been impossible for the method of the prior art to produce super-high-gloss coated papers.
Finishing methods of the prior art capable of producing super-high-gloss coated papers include a cast coating method wherein a coating layer which is substantially wet and is kept in a fluidized condition is brought into pressing contact with a finishing roll having a mirror-like surface to cast the mirror-like surface to the surface of the coating layer, and a brushing method in which the coating layer is finished by means of brushing. The cast coating method is defective in that a great deal of water has to be evaporated during finishing, and it is difficult to release the coating layer from the finishing roll, so that the production rate has to be extremely low. Also, since the moisture contained in the coating layer must move vigorously through the layer while the coating layer passes on the finishing roll, blisters tend to develop in the coating layer particularly in the case of two-side-coated papers. In order to avoid blisters, the coating speed must be further reduced, so that the coated papers produced become very expensive. The brushing method has the defect of being unable to produce coated papers of high smoothness. When this method is used for producing coated papers for printing use, the coated papers produced do not permit printing ink thereon to set quickly, so that the use of the coated papers produced by this method reduces printing efficiency.